1. Field of the Invention
This invention relates to an IC socket having contacts displaceable forwardly to establish a contacted-relation with respect to corresponding terminals of an IC package and displaceable backwardly to cancel the contacted-relation between the contacts and the corresponding terminals, and more particularly to a contacting structure between terminals and contacts.
2. Related Art
In Japanese Patent Publication No. Hei 3-24035, there is disclosed an IC socket in which one pair of pinch-holder pieces raised in parallel relation from a basal portion of each contact such that the pinch-holder pieces are can be resiliently displaced forwardly and backwardly through their own springs. This pinch-holder piece pair pinchingly holds the upper and lower surfaces of the terminals of the IC package, thereby providing an IC socket of a two-point contact structure. At that time, the opposing inner pinch-holder pieces are fixed in a state that resilient force in the opposing direction is accumulated and abutted with lower surfaces of the corresponding terminals, while only the outer pinch-holder pieces are resiliently displaced forwardly and backwardly in response to the upward and downward motion of the contact opening/closing member (canceling member) so as to contact under pressure upper surfaces of the IC terminals when they are displaced forwardly, thereby establishing the two-point contact structure between the inner pinch-holder pieces and the outer pinch-holder pieces.
However, since signals flow through the spring portions of the inner pinch-holder pieces and the spring portions of the outer pinch-holder pieces in the above two-point contact structure, it is practically difficult to design the spring portions equal with lengths in order to fulfill the necessity of obtaining displacing component for a contacted-relation and a contact canceled-relation by the spring portions forming the outer pinch-holder pieces, although the line length and the sectional area of the respective spring portions are desirably equal.
That is, as shown in FIG. 5 of the prior art JP 03-24035 document, it is necessary for the prior art to form a curved spring portion on the outer pinch-holder portion in order to obtain a sufficient spring length and therefore, a significant difference in line length occurs inevitably between the inner pinch-holder piece and the outer pinch-holder piece. As a consequence, electric signals tends to flow through the inner pinch-holder piece having a short line length (spring length), thereby reducing the effect of the two-point contact structure.
On the contrary, if the line length of the inner and outer pinch-holder pieces is designed equal as in FIG. 3 of the prior art JP 3-24035 document, a sufficient length of the spring portion for supporting the outer pinch-holder piece cannot be obtained and the force for operating the canceling member for the purpose of causing the forward and backward displacement in response to the upward and downward motion becomes excessively large, with a result that a permanent deformation occurs due to repeated deformation.
More specifically, as shown in FIGS. 3 and 4 of U.S. Pat. No. 4,691,975 which is based on the prior art, in case both the inner and outer pinch holder-pieces are each provided with a curved spring portion, the line length can be designed equal. However, since the curved spring portions are superimposed, it gives rise to another problem that the contacts and the socket become large in size.
Moreover, in the prior art, no wiping action of the contacts can be expected with respect to the IC terminals, and it is utterly impossible to obtain a wiping action of the contacts with respect to the upper and lower surfaces of the IC terminals.
The present invention has been made in view of the above situation.